JPEG Image Quality in PPT

[JohnNearSyracuse]

I update and make fine tune adjustments to my large PPT presentation
very frequently. (It now is in PPT 2004 for Mac.) I save the same PPT
program a lot. There are over 150 JPEG photo images in the program.
Does saving PPT files frequently as I do have any impact on the image
quality of the JPEG images? I have heard various accounts that JPEG's
can lose sharpness when files are saved, but I would like some
clarification on this please. Perhaps image loss applies only to a
specific JPEG image that is being cropped or edited,and not to the
other slides in the file that is being saved? Please clarify.

 

[Jim Gordon MVP]

Hi John,

Intersting question!

When you put an image file into PowerPoint it stores the copy within the
presentation. Because PowerPoint does not save a file of the JPEG there
will be no loss of quality by saving and re-saving the presentation.

But you have heard correctly. JPEG is a "lossy" format. That means each
time you open and then save a JPEG image using a picture image editor
(eg. PhotoShop or Graphic Converter) you lose some of the fidelity of
the image - even if you use the highest quality setting. So if you want
to have "master" copies of images that are sure to not lose quality when
they are saved select a "lossless" file format, such as TIFF.

Here's a detailed list of file formats and their characteristics:
http://en.wikipedia.org/wiki/List_of_file_formats

-Jim

 

[Steve Rindsberg]

I update and make fine tune adjustments to my large PPT presentation
very frequently. (It now is in PPT 2004 for Mac.) I save the same PPT
program a lot. There are over 150 JPEG photo images in the program.
Does saving PPT files frequently as I do have any impact on the image
quality of the JPEG images?

No, no worries there. PowerPoint doesn't do anything with the JPGs other than
display them; they stay in PPT just as they originally were when you inserted
them. It's opening, *editing* and resaving JPGs that makes them turn on you.


================================================
Steve Rindsberg, PPT MVP
PPT FAQ: www.pptfaq.com
PPTools: www.pptools.com
================================================

 

[JohnNearSyracuse]

Jim, thank you for the clarification. I have worried about those JPG
images in my presentation for a long time ! Does "editing" JPG's
include compressing them to save file space? Since I do not have the
compression feature that I had in PPT 2002, I will need to resort to
another method to decrease the file size of some new digital photos I
just purchased.

 

[JohnNearSyracuse]

PS, Jim and Steve, thank you both for your helpful responses.
John

 

[Steve Rindsberg]

Jim, thank you for the clarification. I have worried about those JPG
images in my presentation for a long time ! Does "editing" JPG's
include compressing them to save file space? Since I do not have the
compression feature that I had in PPT 2002, I will need to resort to
another method to decrease the file size of some new digital photos I
just purchased.

Anything that changes the data in the file (including compressing) will tend to
affect the quality (unless it uses lossless compression, which I think JPG also
supports). If your photos are already in JPG format, you may want to convert
to PNG or TIFF as a kind of "master" copy, then do any further
editing/resampling/etc. on those and finally as a last step, save to JPG.

================================================
Steve Rindsberg, PPT MVP
PPT FAQ: www.pptfaq.com
PPTools: www.pptools.com
================================================